The present invention relates to a solid golf ball produced by injection-molding a thermoplastic urethane resin relatively thinly around a core made from a rubber material.
Golf balls using covers made from thermoplastic urethane resins (hereinafter, often referred to simply “urethane covers”) have been proposed. In the process of producing such a golf ball, it is recommended to form the urethane cover by injection molding from the viewpoint of easy molding. The injection molding for forming the urethane cover, however, has an inconvenience that the urethane cover material can be relatively easily injection-molded around a relatively smooth surface of a core made from an ionomer resin or a polyester elastomer, but is difficult to be thinly injection-molded around a rough surface of a core made from a rubber material. For example, it is easy to form an urethane cover having a relatively large thickness (for example. 1.9 mm or more) around a core made from a rubber material by injection molding, but it is difficult to form an urethane cover having a small thickness (for example, 0.8 mm or less) around a core made from a rubber material by injection molding.
To be more specific, at the time of injection-molding an urethane cover material around a core having a rough surface, it becomes often impossible for the cover material to sufficiently go round about the core. This is because the urethane cover material is affected by the rough surface of the cover and is thereby not uniformly injected around the core. In this case, since the cover material is not uniformly injected around the core, there may occur a phenomenon that air in a mold remains on the surface of the golf ball. In addition, if the core is largely deformed, it is also difficult to uniformly inject the cover material around the core.